A number of diseases, illnesses and other medical conditions are treatable at least in part by dilatation of a bone, tissue or duct. For example, medical conditions and/or physical injuries can lead to or predispose a bone to deformity, such as a fracture. A familiar example is osteoporosis, in which bones lose calcium and break more easily. The human spinal column, comprised of interconnected vertebrae or vertebral bodies, has proven to be especially susceptible to the effects of osteoporosis. A vertebral body weakened by osteoporosis can fracture from a fall, or simply during routine activities. When a vertebral body fractures, it can collapse and change the shape of the spine. The damaged portion of the spine becomes shorter, and the rest of the spine above the broken vertebral body bends forward. As additional vertebral fractures occur, the spine shortens further, increasingly forcing the individual into a hunched-over posture.
As taught by U.S. Pat. No. 6,248,110 (Reiley et al.), U.S. Pat. No. 6,235,043 (Reiley et al.) and U.S. Pat. No. 6,066,154 (Reiley et al.), each of which is incorporated herein in its entirety by reference, it is known in the art to use expandable bodies, such as a balloon element, to treat certain bone conditions, resulting from osteoporosis, avascular necrosis, bone cancer and the like, that predispose a bone to, or lead to, fracture or collapse. A particularly common application is in the treatment of vertebral body compression fractures resulting from osteoporosis, as taught for example by U.S. Pat. No. 6,719,773 (Boucher et al.) and U.S. Pat. Publ. No. 2008/0140084 (Osorio et al.), each of which is incorporated herein in its entirety by reference.
Typical treatment of such conditions includes a series of steps which a surgeon or health care provider can perform to form a cavity in an interior region of pathological bone, including but not limited to osteoporotic bone, osteoporotic fractured metaphyseal and epiphyseal bone, osteoporotic vertebral bodies, fractured osteoporotic vertebral bodies, fractures of vertebral bodies due to tumors especially round cell tumors, avascular necrosis of the epiphyses of long bones, especially avascular necrosis of the proximal femur, distal femur and proximal humerus and defects arising from endocrine conditions.
The method typically further includes the steps of making an incision in the skin (usually one incision, but a second small incision may also be required if a suction egress is used) followed by the placement of a guide pin which is passed through the soft tissue down to and into the bone.
The method of the Reiley '154 patent, for example, further includes the steps of drilling the bone to be treated to form a cavity or passage in the bone, following which an inflatable balloon-like device is inserted into the cavity or passage where it is inflated. The inflation of the inflatable device causes a compacting of the cancellous bone and bone marrow against the inner surface of the cortical wall of the bone to further enlarge the cavity or passage. The inflatable device is then deflated and then is completely removed from the bone. The art further teaches that a smaller inflatable device (a starter balloon) can be used initially, if needed, to initiate the compacting of the bone marrow and to commence the formation of the cavity or passage in the cancellous bone and marrow. After this has occurred, a larger, inflatable device can be inserted into the cavity or passage to further compact the bone marrow in all directions.
Next in accordance with Reiley '154, a flowable biocompatible filling material, such as methylmethacrylate cement or a synthetic bone substitute, is directed into the bone cavity or passage that has been formed and enlarged, and the filling material is allowed to set to a hardened condition to provide ongoing structural support for the bone. Following this latter step, the insertion instruments are removed from the body and the incision in the skin is covered with a bandage.
A related U.S. Pat. No. 6,048,346 (Reiley et al.), which is also incorporated herein in its entirety by reference, teaches an improved mechanical bone cement injection assembly, which is described as constituting an improvement over prior art devices that operated “similar to a household caulking gun” in that it facilitates greater control over the placement of cement and other flowable liquids into an interior region of a bone.
Another inflatable apparatus intended for deployment into interior body regions is described in U.S. Pat. No. 5,972,015 (Scribner et al.), which is also incorporated herein in its entirety by reference. The Scribner '015 patent describes a catheter tube extending along a first axis in conjunction with an expandable structure having an expanded geometry oriented about a second axis, not aligned with the first axis, so as to treat an asymmetrically-shaped interior body region or where the access channel cannot be aligned with the body region to be treated. A particular application of this technology is stated to be for the fixation of fractures or other osteoporotic and non-osteoporotic conditions of human and animal bones, specifically for treating a human lumbar vertebra.
Two somewhat earlier patents describing similar apparatus and methods for treating vertebral body compression fractures and the like using an inflatable balloon-like element inserted into the bone cavity are U.S. Pat. No. 5,108,404 (Scholten et al.) and U.S. Pat. No. 4,969,888 (Scholten et al.), each of which is also incorporated herein in its entirety by reference.
In additional embodiments of known technologies for treating bone structures, U.S. Pat. No. 6,613,054 (Scribner et al.) and U.S. Pat. No. 6,241,734 (Scribner et al.), each of which is incorporated herein in its entirety by reference, describe systems and methods for advancing a tamping instrument through a cannula that has been deployed to establish a subcutaneous channel into bone. Material is introduced into the bone through the cannula, and the tamping instrument is used to move material in the cannula into the bone.
Numerous problems remain, however, with the prior art systems and methods. For successful expansion of a fractured vertebral body, an expandable element inserted into the vertebral cavity must be capable of being inflated to a relatively large working diameter of about 12 mm-25 mm, starting with a relatively short balloon working length, e.g., about 10 mm-25 mm, sized to fit inside the vertebral cavity, at very high working pressures on the order of 200-450 psi or higher. Use of lower inflation pressure in such applications may result in only a partial, incomplete expansion of a fractured vertebral body. When that partially-expanded vertebral body is subsequently filled with cement or comparable material, which then hardens, there is a permanent remaining spinal deformity at that vertebral body. Not only must the expandable/inflatable element in the vertebral cavity be capable of inflation to very high pressure without rupture in order to fully expand a collapsed/fractured vertebral body, in addition the inflated element must resist puncture by hard, sharp cancellous bone and surface irregularities around the outer edges of the vertebral cavity. Medical protocols have been developed for this type of vertebral fracture treatment, including specifying standards for the minimum recommended thickness of the balloon or expandable element in order to provide a safeguard and a margin of error against puncture/rupture of the balloon during a treatment procedure.
The following detailed description of the expandable structure for a preferred assembly for medical procedures to compact cancellous bone for the fixation of bone fractures appears in U.S. Pat. No. 6,719,773 (Boucher '773) at col. 8, line 64 to col. 12, line 17:
A. The Expandable Structure. The material from which the structure 56 is made should possess various physical and mechanical properties to optimize its functional capabilities to compact cancellous bone. Important properties for the structure include one or more of the following: (1) the ability to expand in volume; (2) the ability to deform in a desired way when expanding and assume a desired shape inside bone; and/or (3) the ability to withstand abrasion, tearing, and puncture when in contact with cancellous and/or cortical bone.
1. Expansion Property. A first desired property for the structure material is the ability to expand or otherwise increase in volume without failure. This property enables the structure 56 to be deployed in a collapsed, low profile condition subcutaneously, e.g., through a cannula, into the targeted bone region. This property also enables the expansion of the structure 56 inside the targeted bone region to press against and compress surrounding cancellous bone, or move cortical bone to a prefracture or other desired condition, or both.
The desired expansion property for the structure material can be characterized in one way by ultimate elongation properties, which indicate the degree of expansion that the material can accommodate prior to failure. Sufficient ultimate elongation permits the structure 56 to compact cortical bone, as well as lift contiguous cortical bone, if necessary, prior to wall failure. Desirably, the structure 56 will comprise material able to undergo an ultimate elongation of at least 50%, prior to wall failure, when expanded outside of bone. More desirably, the structure will comprise material able to undergo an ultimate elongation of at least 150%, prior to wall failure, when expanded outside of bone. Most desirably, the structure will comprise material able to undergo an ultimate elongation of at least 300%, prior to wall failure, when expanded outside of bone.
Alternatively, the structure material can comprise one or more non-compliant or partially compliant materials having substantially lower ultimate elongation properties, including, but not limited to, kevlar, aluminum, nylon, polyethylene, polyethyiene-terephthalate (PET) or mylar. Such a structure would desirably be initially formed to a desired shape and volume, and then contracted to a collapsed, low profile condition for introduction through a cannula into the targeted bone region. The structure could then be expanded to the desired shape and volume to press against and compress surrounding cancellous bone and/or move cortical bone to a prefracture or desired condition, or both. As another alternative, the structure could comprise a combination of non-compliant, partially compliant and/or compliant materials.
2. Shape Property. A second desired property for the material of the structure 56, either alone or in combination with the other described properties, is the ability to predictably deform during expansion, so that the structure 56 consistently achieves a desired shape inside bone.
The shape of the structure 56, when expanded in bone, is desirably selected by the physician, taking into account the morphology and geometry of the site to be treated. The shape of the cancellous bone to be compressed and/or cortical bone to be displaced, and the local structures that could be harmed if bone were moved inappropriately, are generally understood by medical professionals using textbooks of human skeletal anatomy along with their knowledge of the site and its disease or injury, and also taking into account the teachings of U.S. patent application Ser. No. 08/788,786, filed Jan. 23, 1997, and entitled “Improved Inflatable Device for Use in Surgical Protocol Relating to Fixation of Bone,” which is incorporated herein by reference. The physician is also desirably able to select the desired expanded shape inside bone based upon prior analysis of the morphology of the targeted bone using, for example, plain film x-ray, fluoroscopic x-ray, or MRI or CT scanning.
Where compression of cancellous bone and/or cavity creation is desired, the expanded shape inside bone is selected to optimize the formation of a cavity that, when filled with a selected material, provides support across the region of the bone being treated. The selected expanded shape is made by evaluation of the predicted deformation that will occur with increased volume due to the shape and physiology of the targeted bone region.
Where displacement of cortical bone is desired, the expanded shape can be selected to optimize displacement of the cortical bone in the desired direction(s), as well as to distribute forces in a desired manner across the targeted cortical bone region. If desired, the structure can be designed to distribute forces evenly and/or uniformly across the targeted cortical bone region. Alternatively, the structure can be designed to impart a maximum force on a specific area of the cortical bone so as to cause desired fracture and/or maximum displacement of specific cortical bone regions.
In some instances, it is desirable, when creating a cavity, to also move or displace the cortical bone to achieve the desired therapeutic result. Such movement is not per se harmful, as that term is used in this Specification, because it is indicated to achieve the desired therapeutic result. By definition, harm results when expansion of the structure 56 results in a worsening of the overall condition of the bone and surrounding anatomic structures, for example, by injury to surrounding tissue or causing a permanent adverse change in bone biomechanics.
As one general consideration, in cases where the bone disease causing fracture (or the risk of fracture) is the loss of cancellous bone mass (as in osteoporosis), the selection of the expanded shape of the structure 56 inside bone should take into account the cancellous bone volume which should be compacted to achieve the desired therapeutic result. An exemplary range is about 30% to 90% of the cancellous bone volume, but the range can vary depending upon the targeted bone region. Generally speaking, compacting less of the cancellous bone volume leaves more uncompacted, diseased cancellous bone at the treatment site.
Another general guideline for the selection of the expanded shape of the structure 56 inside bone is the amount that the targeted fractured bone region has been displaced or depressed. The expansion of the structure 56 inside a bone can elevate or push the fractured cortical wall back to or near its anatomic position occupied before fracture occurred.
For practical reasons, it is often desired that the expanded shape of the structure 56 inside bone, when in contact with cancellous bone, substantially conforms to the shape of the structure 56 outside bone, when in an open air environment. This allows the physician to select in an open air environment a structure having an expanded shape desired to meet the targeted therapeutic result, with the confidence that the expanded shape inside bone will be similar in important respects.
An optimal degree of shaping can be achieved by material selection and by special manufacturing techniques, e.g., thermoforming or blow molding, as will be described in greater detail later.
In some instances, it may not be necessary or desired for the structure to predictably deform and/or assume a desired shape during expansion inside bone. Rather, it may be preferred that the structure expand in a substantially uncontrolled manner, rather than being constrained in its expansion. For example, where compaction of weaker sections of the cancellous bone is desired, it may be preferred that the structure initially expand towards weaker areas within the bone. In such cases, the structure can be formed without the previously-described shape and/or size, and the expanded shape and/or size of the structure can be predominantly determined by the morphology and geometry of the treated bone.
3. Toughness Property. A third desired property for the structure 56, either alone or in combination with one or more of the other described properties, is the ability to resist surface abrasion, tearing, and puncture when in contact with cancellous bone. This property can be characterized in various ways.
One way of measuring a material's resistance to abrasion, tearing and/or puncture is by a Taber Abrasion test. A Taber Abrasion test evaluates the resistance of a material to abrasive wear. For example, in a Taber Abrasion test configured with an H-18 abrasive wheel and a 1 kg load for 1000 cycles (ASTM Test Method D 3489), Texin® 5270 material exhibits a Taber Abrasion value of approximately 75 mg loss. As another example, under the same conditions Texin® 5286 material exhibits a Taber Abrasion value of approximately 30 mg loss. Typically, a lower Taber Abrasion value indicates a greater resistance to abrasion. Desirably, one embodiment of the structure will comprise material having a Taber Abrasion value under these conditions of less than approximately 200 mg loss. More desirably, the structure will comprise material having a Taber Abrasion value under these conditions of less than approximately 145 mg loss. Most desirably, the structure will comprise material having a Taber Abrasion value under these conditions of less than approximately 90 mg loss. Of course, materials having a Taber Abrasion value of greater than or equal to 200 mg loss may be utilized to accomplish some or all of the objectives of the present invention.
Another way of measuring a material's resistance to abrasion, tearing and/or puncture is by Elmendorf Tear Strength. For example, under ASTM Test Method D 624, Texin® 5270 material exhibits a Tear Strength of 1,100 lb-ft/in. As another example, under the same conditions, Texin® 5286 exhibits a Tear Strength of 500 lb-ft/in. Typically, a higher Tear Strength indicates a greater resistance to tearing. Desirably, an alternate embodiment of the structure will comprise material having a Tear Strength under these conditions of at least approximately 150 lb-ft/in. More desirably, the structure will comprise material having a Tear Strength under these conditions of at least approximately 220 lb-ft/in. Most desirably, the structure will comprise material having a Tear Strength under these conditions of at least approximately 280 lb-ft/in. Of course, materials having a Tear Strength of less than or equal to 150 lb-ft/in may be utilized to accomplish some or all of the objectives of the present invention.
Another way of measuring a material's resistance to abrasion, tearing and/or puncture is by Shore Hardness. For example, under ASTM Test Method D 2240, Texin® 5270 material exhibits a Shore Hardness of 70 D. As another example, under the same conditions, Texin® 5286 material exhibits a Shore Hardness of 86 A. Typically, a lower Shore Hardness number on a given scale indicates a greater degree of elasticity, flexibility and ductility. Desirably, another alternate embodiment of the structure will comprise material having a Shore Hardness under these conditions of less than approximately 75 D. More desirably, the structure will comprise material having a Shore Hardness under these conditions of less than approximately 65 D. Most desirably, the structure will comprise material having a Shore Hardness under these conditions of less than approximately 100 A. Of course, materials having a Shore Hardness of greater than or equal to 75 D may be utilized to accomplish some or all of the objectives of the present invention.
It should also be noted that another alternate embodiment of a structure incorporating a plurality of materials, such as layered materials and/or composites, may possess significant resistance to surface abrasion, tearing and puncture. For example, a layered expandable structure incorporating an inner body formed of material having a Taber Abrasion value of greater than 200 mg loss and an outer body having a shore hardness of greater than 75 D might possess significant resistance to surface abrasion, tearing and puncture. Similarly, other combinations of materials could possess the desired toughness to accomplish the desired goal of compressing cancellous bone and/or moving cortical bone prior to material failure.
One possible approach to improve the strength of the balloon-like elements to make them better able to withstand very high inflation pressures would be to use thicker balloon walls and/or to make these elements out of stiffer, stronger materials. There are several reasons, however, why these seemingly straightforward solutions have not proven successful in practice. One is the need to limit the balloon wall thickness and the need to maintain balloon wall flexibility to facilitate access to, and withdrawal from, a bone cavity.
In treating a vertebral fracture, for example, the vertebral cavity is typically accessed by drilling a small hole and locating a short, hollow, metallic tubular element (i.e., a hollow sleeve or cannula) through the left or right pedicle portion (or sometimes both) of the vertebral arch (see, e.g., FIG. 2 of U.S. Pat. No. 5,972,015, which shows the left and right pedicle portions 42 of vertebral arch 40, and FIG. 6 of the same patent which shows an access hole for catheter tube 50 and expandable structure 56 through one pedicle portion 42 into the interior volume 30 of reticulated cancellous, or spongy, bone 32). Because pedicle portion 42 shown in FIGS. 2 and 6 of the Scribner '015 patent is relatively small and is itself readily susceptible to fracture if its structural integrity is impaired by too large a hole, it is crucial to keep the diameter of the hole, therefore also of the cannula, to a minimum, typically no larger than about 4-5 mm. Indeed, as taught hereinafter, it has become desirable based on current medical practice to use an opening made by an 11-gauge needle with a diameter of only about 0.121 inches (about 3.06 mm) or less, thereby requiring the use of an 11-gauge needle cannula. The cannula helps to protect surrounding bone portions from abrasion and from expansion forces while inserting or removing the catheter shaft or while inflating the balloon element that is bonded to the distal end of the catheter shaft.
Because of the narrow interior diameter of the cannula used in these applications, it was typical to fold or wrap the balloon-like element relatively tightly at the distal end of an associated catheter shaft in order to keep the maximum diameter of the unit at the balloon end small enough to fit through the cannula of a small-diameter pedicle hole. An expandable element fabricated with relatively thick walls and/or made from a relatively stiff, less flexible material might be inflatable to a higher pressure, but these characteristics could impede folding or wrapping the element tightly enough to fit through the cannula of a narrow-diameter pedicle opening. For these reasons, balloon elements for bone dilatation procedures would typically have thicker walls compared, for example, to the balloon elements commonly used for angioplasty procedures, but the bone dilatation balloons would generally be fabricated from more flexible, elastic materials than those used in angioplasty procedures.
Even if a balloon element can be wrapped or folded sufficiently tightly for insertion through the cannula of a narrow-diameter pedicle hole, it can later be difficult to remove or withdraw that balloon element through the same cannula following a dilatation procedure because, after a cycle of inflation and deflation inside a vertebral cavity, a balloon element may not be able to be refolded or rewrapped in-situ to its previously folded size or to a size sufficiently small to be withdrawn through the cannula without the use of excessive force which might crack or break the pedicle or tear the balloon from the catheter.
These problems were addressed, at least in part, by U.S. Pat. No. 7,488,337 (Saab et al.), which is incorporated herein in its entirety by reference. Saab '337 describes techniques for tensioning, stretching, folding and/or wrapping the expandable elements of devices designed for bone dilatation procedures to better facilitate insertion of the expandable elements into and, after an inflation procedure, withdrawal of the expandable elements from a bone structure through a narrow diameter cannula.
As noted above, however, the trend in medical practice in this field has been to utilize the smallest possible diameter hole or holes through the exterior portion of the bone to access the bone interior region. Current practice is to use an 11-gauge needle in order to perform a vertebral treatment, if possible, using bone openings that are so small (about 0.120 inches) that they can only accommodate an eleven (11) gauge cannula. Currently available catheter/expandable element apparatus for such bone treatment procedures, however, cannot be inserted into and later, following a treatment procedure, withdrawn from a bone dilatation site through a standard wall 11-gauge cannula (which typically has an inside diameter of only 0.094 inches±0.002 inches). For example, the Osorio '084 patent publication cited above contemplates use of an 11-gauge needle for performing a vertebral fracture treatment. But, in Osorio '084, after dilating the bone structure, the expandable structure is left in place and filled with cement or comparable material. Thus, Osorio '084 does not contemplate or address the problem of removing the expandable structure through the very small interior of an 11-gauge cannula following an inflation/deflation cycle.
By contrast with an 11-gauge cannula, a thin-walled 10-gauge needle cannula (having a thinner wall thickness than a “standard” 10G cannula), which has become the industry standard for Kyphoplasty procedures, has an inside diameter of 0.114 inches (2.89 mm). The thin-walled 10-gauge cannula and its 0.114 inch inside diameter can accommodate current catheter assemblies used in these procedures, but it also has a larger outside diameter of about 0.134 inches that cannot fit inside a bone opening of only about 0.121 inches, which is the size of the opening made with an 11-gauge needle.
But, adapting the technology in this field to a smaller 11-gauge cannula, having an inside diameter (ID) of about 0.094 inches (2.39 mm)±0.002 inches and an outside diameter (OD) of about 0.120 inches (3.05 mm)±0.001 inches involves many substantial technological challenges. Much more is involved in this adaptation than just slightly shrinking all of the standard apparatus components.
First, because the volume of the bone interior that needs expanding remains unchanged, the expandable element must still be capable of expanding to that necessary bone interior volume, but that expandable element also needs to fit through the smaller interior diameter of an 11-gauge cannula. One approach to facilitate the insertion and removal steps with the larger, conventional 8-gauge and 10-gauge cannulas is to provide a slippery, friction-reducing coating or lubricating fluid (such as a silicone material) along the interior of the cannula, on the exterior of the expandable element, or both, to reduce friction and facilitate sliding the expandable element through the cannula.
A potential problem with this lubricant coating approach, however, is that at least a portion of such a lubricant would be transferred via the expandable element into the interior of the bone, where it would remain as a foreign contaminant. The presence of such a contaminant might cause irritation or an adverse body reaction at the interior bone site. In addition, the presence of a lubricating substance coating the walls of the expanded cavity of the bone following a dilatation procedure can possibly prevent a subsequently injected cement material from solidly and effectively bonding to the bone interior.
It also is not currently feasible to facilitate the use of an 11-gauge cannula in these procedures by reducing the wall thickness of the expandable element. As discussed above, the expandable element needs to withstand inflation to relatively high pressure without being punctured by irregularities or projecting portions of the bone interior. Furthermore, current medical protocols for bone dilatation procedures using an expandable balloon prescribe the minimum acceptable wall thickness for the expandable element, and those protocols must be met whether the balloon element needs to fit through the interior of a conventional 8-gauge or 10-gauge cannula, or through a very narrow diameter 11-gauge cannula.
Structural integrity and materials issues for the cannula create another significant design constraint. A “standard” 11-gauge cannula has an interior diameter (ID) of 0.094 inches with a tolerance of ±0.002 inches (i.e., an interior diameter that may range from 0.092 to 0.096 inches) and an outer diameter (OD) ranging from 0.119 to 0.121 inches (about 3.05 mm). In theory, one could make an ultra-thin walled 11-gauge cannula with an interior diameter of about 0.114 inches (i.e., comparable to a thin-walled 10-gauge cannula) but with a very thin wall such that the outer diameter was only about 0.120 inches. But, such an ultra-thin wall of only about 0.003 inches would compromise the structural integrity of the cannula which must function under demanding operating conditions. Such a modification would therefore raise numerous patient safety issues.
Another performance issue in this field is being able to accurately monitor the location of the expandable element as it is slid through the cannula and into the interior region of the bone that is being treated. This is an important issue because the length (along the catheter axis) of the expandable element (before inflation) is carefully selected to correspond to the size of the bone interior when the element is fully inflated.
Because of these narrow tolerances, it is important that the expandable element be properly situated in the bone interior before an inflation procedure is initiated. If the expandable element is pushed too hard and too far into the bone interior region, the distal tip of the catheter/expandable element may damage or even rupture the distal wall of the bone interior region. On the other hand, if the proximal portion of the expandable element is still located inside the cannula when the inflation procedure is started, the expandable element will be unable to fully inflate and, thus, unable to fully dilate the bone interior.
One approach to addressing the expandable element positioning problem has been to place radiopaque markings at one or more locations inside the expandable element and, using appropriate fluoroscopy equipment, to monitor the location of the expandable element by means of those markings as it is slid through the cannula and into the interior of the bone structure. Although the thickness of such radiopaque markings is generally very small, even that small added thickness becomes a significant factor in the context of wrapping or folding a full-sized bone dilatation expandable element to fit through the very small inside diameter of an 11-gauge cannula.
Yet another factor that becomes significant in the context of fitting a full-sized bone dilatation expandable element through the interior of an 11-gauge cannula is the juncture where the proximal end of the expandable element is secured to the distal end of the catheter shaft on which the expandable element is carried. Typically, the opening at the proximal end of the expandable element is formed slightly larger than the exterior diameter of the distal end of the catheter shaft. Thus, the proximal end of the expandable element can be slid over the distal end of the catheter shaft, and the expandable element can then be sealed to the end of the shaft by gluing, thermal bonding, or using similar sealing techniques. The result of this bonding procedure, however, is typically a small section of enlarged diameter at the juncture between the two components, and such an enlarged diameter section of the combined apparatus can inhibit passage of the expandable element through the interior of an 11-gauge cannula.
Still another design constraint of conventional expandable element bone dilatation systems is the use of a catheter shaft having an annular configuration with concentric inner and outer lumens. This coaxial, dual-lumen structure permits the outer lumen to be used for flowing a fluid (such as air, water or contrast fluid) to or from the expandable element for inflating or deflating the element once it is in place inside the bone, while using the separate inner lumen (which extends to the interior distal end of the expandable element) to contain a mandrel, rod or similar component. The mandrel may be moveable and slidable axially along the axis of the catheter assembly and may extend the length of the inner lumen into and to the distal end of the inner lumen and the expandable element.
At the same time, however, the separate, concentric lumen structure of such a catheter shaft takes up additional space and requires a larger diameter catheter shaft to achieve a given degree of cross-sectional area for fluid flow to/from the expandable element. In addition, this design generally increases the size of the wrapped or folded expandable element because in these configurations the inner catheter lumen typically extends through the interior of the expandable element.
These and other deficiencies in and limitations of the above-described prior art approaches to treating bone deformities, such as vertebral body compression fractures, and other medical treatments involving inserting and inflating an expandable element through a narrow cannula are overcome in whole or in part with the systems, apparatus and methods of this invention.